Japanese Patent Application Laid-Open (kokai) No. H10-152014 discloses a conventional activation control apparatus for an occupant protection apparatus. The conventional activation control apparatus includes satellite sensors provided on left front and right front portions of a vehicle, and a floor sensor provided at a central portion of the vehicle body. The activation control apparatus is configured to lower an airbag activation threshold of the floor sensor when one or more of the satellite sensors detects an impact equal to or greater than a predetermined reference value. Further, when the satellite sensor(s) detects an impact equal to or greater than the predetermined reference value, the conventional activation control apparatus determines that the severity of impact is high, and controls activation of the occupant protection apparatus.
Japanese Patent Application Laid-Open (kokai) No. 2000-219098 discloses another conventional activation control apparatus for an occupant protection apparatus. The conventional activation control apparatus includes front sensors provided on left front and right front portions of a vehicle, a floor sensor provided at a central portion of the vehicle body, and an output value control section for controlling output of an inflator, which activates an airbag unit on the basis of detection values from these sensors. The output value control section determines the nature of a collision on the basis of detection values from these sensors, and optimizes the output of the inflator in accordance with the determined nature of the collision.
Japanese Patent Application Laid-Open (kokai) No. 2002-104130 discloses still another conventional activation control apparatus for an occupant protection apparatus. The conventional activation control apparatus also includes satellite sensors provided on left front and right front portions of a vehicle, and a floor sensor provided at a central portion of the vehicle body. The activation control apparatus determines a value from the relation between a deceleration determined on the basis of an output signal of the floor sensor and a velocity obtained through time integration of the deceleration, and, when the determined value exceeds a threshold variation pattern for output use, increases activation output at the time of activation of an airbag unit. The activation control apparatus further determines a second value from the relation between a deceleration determined on the basis of output signals of the satellite sensors and the above-mentioned velocity, and, when the determined second value exceeds a predetermined threshold, replaces the threshold variation pattern for output use with a different pattern of lower threshold.
In the above-described conventional activation control apparatuses for an occupant protection apparatus, severity of impact caused by a collision of a vehicle is determined on the basis of detection values representing decelerations stemming from the collision and detected by means of satellite sensors (front sensors) provided at the front portion of the vehicle and a floor sensor provided at the central portion of the vehicle body. On the basis of the determined severity, activation of an airbag unit is controlled (between high output and low output).
However, even in collisions which are of substantially equal severity, activation of an airbag unit must be controlled in different manners in accordance with the nature of a collision between a vehicle and an object; i.e., depending on whether the collision is a symmetric collision (head-on collision, collision with a pole (hereinafter referred to as a “pole collision”), underride collision, etc.) or an asymmetrical collision (oblique collision, offset collision, etc.), because the time of deceleration stemming from a collision of a vehicle changes depending on the nature of the collision. Therefore, desire has arisen for optimally controlling activation of an airbag unit in accordance with the nature of a collision between a vehicle and an object.